The concept of coronary capillary reserve for transport of metabolites has evolved only recently. Further experimental evidence is required to firmly establish this notion. It is proposed to evaluate the adaptive control of coronary microvascular flow and transport to metabolic and functional requirements of the normal myocardium. The dynamics of capillary transport and microvascular flow will be investigated by a series of physiological and morphological methods including multiple tracer dilution techniques, radioactively labeled microspheres, labeling of capillaries by infusion of intravascular tracers and by cytochemical reactions for histological examination, and by myocardial casting with low visocosity silicone elastomers. The results of this research project will provide basis to analyze physiologically and morphologically the fundamental relations between transport and flow in the myocardium. It is submitted that this project will also provide a basis for analyzing pathophysiologic states of the heart such as the postoperative derangements of the performance of the left ventricle which contribute to the morbidity and mortality observed after surgical correction of valvular heart disease.